Synthesis, characterization, thermo- and photoluminescence properties of Bi3+ co-doped Gd2O3:Eu3+ nanophosphors

Gd2O3:Eu3+ (4 mol%) co-doped with Bi3+ (Bi = 0, 1, 3, 5, 7, 9 and 11 mol%) ions were synthesized by a low-temperature solution combustion method. The powders were calcined at 800A degrees C and were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared and UV-Vis spectroscopy. The PXRD profiles confirm that the calcined products were in monoclinic with little cubic phases. The particle sizes were estimated using Scherrer's method and Williamson-Hall plots and are found to be in the ranges 40-60 nm and 30-80 nm, respectively. The results are in good agreement with TEM results. The photoluminescence spectra of the synthesized phosphors excited with 230 nm show emission peaks at similar to 590, 612 and 625 nm, which are due to the transitions D-5(0)-> F-7(0), D-5(0)-> F-7(2) and D-5(0)-> F-7(3) of Eu3+, respectively. It is observed that a significant quenching of Eu3+ emission was observed under 230 nm excitation when Bi3+ was co-doped. On the other hand, upon 350 nm excitation, the luminescent intensity of Eu3+ ions was enhanced by incorporation of Bi3+ (5 mol%) ions. The introduction of Bi3+ ions broadened the excitation band of Eu3+ of which a new strong band occurred ranging from 320 to 380 nm. This has been attributed to the 6s(2)-> 6s6p transition of Bi3+ ions, implying a very efficient energy transfer from Bi3+ ions to Eu3+ ions. The gamma radiation response of Gd2O3:Eu3+ exhibited a dosimetrically useful glow peak at 380A degrees C. Using thermoluminescence glow peaks, the trap parameters have been evaluated and discussed. The observed emission characteristics and energy transfer indicate that Gd2O3:Eu3+, Bi3+ phosphors have promising applications in solid-state lighting.

Effect of different fuels on structural, thermo and photoluminescent properties of Gd 2O 3 nanoparticles

Gd 2O 3 nanoparticles (27-60nm) have been synthesized by the low temperature solution combustion method using citric acid, urea, glycine and oxalyl dihydrazide (ODH) as fuels in a short time. The structural and luminescence properties have been carried out using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman, UV-Vis, photoluminescence (PL) and thermoluminescence (TL) techniques. The optical band gap values were estimated for as formed and 800°C calcined samples. The band gap values in as-formed and calcined samples were found to be in the range 4.89-5.59eV. It is observed that, the band gap values are lower for as-formed products and it has been attributed to high degree of structural defects. However, in calcined samples, structure becomes more order with reduced structure defects. Upon 270nm excitation, deep blue UV-band at �390nm along with blue (420-482nm), green (532nm) and red emission (612nm) was observed. The 390nm emission peak may be attributed to recombination of delocalized electron close to the conduction band with a single charged state of surface oxygen vacancy. TL measurements were carried out on Gd 2O 3 prepared by different fuels by irradiating with γ-rays (1kGy). A well resolved glow peak at 230°C was observed for all the samples. It is observed that TL intensity is found to be higher in for urea fuel when compared to others. From TL glow curves the kinetic parameters were estimated using Chen's peak shape method and results are discussed in detail. © 2012 Elsevier B.V.

Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO2) nano-photocatalysts, with different phases, prepared using a modified sol-gel process were employed in the degradation of rhodamine at 10 mg L-1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450 degrees C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K-app) of 0.023 min(-1). The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024 min(-1) for 450, 500, 550 and 600 degrees C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017 min(-1), which is similar to that of the commercial titania.

Effect of Calcination Temperature on Structural, Photoluminescence, and Thermo luminescence Properties of Y2O3:Eu3+ Nanophosphor

Red light emitting cubic Y1.95Eu0.05O3 nanophosphors have been synthesized by a low temperature solution combustion method using ethylene diamine tetra acetic acid (EDTA) as fuel. The systematic studies on the effect of calcination temperature on its structural, photoluminescence (PL), and thermoluminescence (TL) properties were reported. The crystallinity of the samples increases, and the strain is reduced with increasing calcination temperature. SEM micrographs reveal that samples lose their porous nature with an increase in calcination temperature. PL spectra show that the intensity of the red emission (611 nm) is highly dependent on the calcination temperature and is found to be 10 times higher when compared to as-formed samples. The optical band gap (E-g) was found to reduce with an increase of calcination temperature due to reduction of surface defects. The thermoluminescence (TL) intensity was found to be much enhanced in the 1000 degrees C calcined sample. The increase of PL and TL intensity with calcination temperature is attributed to the decrease of the nonradiative recombination probability, which occurs through the elimination of quenching defects. The trap parameters (E, b, s) were estimated from Chen's glow peak shape method and are discussed in detail for their possible usage in dosimetry.

YGa1-xMnxO3: A novel purple inorganic pigment

A purple inorganic pigment, YGa1-xMnxO3 (0 < x <= 0.10), based on hexagonal YGaO3 is reported here. The metastable series of oxides were prepared by a sol-gel technique where the dried gels, obtained from aqueous solutions of metal nitrate-citric acid mixtures, were calcined for a short duration in a preheated furnace around 850 degrees C. The purple colour of the oxides arises from the specific trigonal bipyramidal ligand field around Mn-III in a YGaO3 host. Other hexagonal RGaO3 hosts for R = Lu, Tm and Ho substituted with Mn-III also produce similar purple coloured materials.

Exchange-spring mechanism of soft and hard ferrite nanocomposites

The paper reports exchange-spring soft and hard ferrite nanocomposites synthesized by chemical co-precipitation with or without the application of ultrasonic vibration. The composites contained BaFe12O19 as the hard phase and CoFe2O4/MgFe2O4 as the soft phase. X-ray diffraction patterns of the samples in the optimum calcined condition indicated the presence of soft ferrites as face-centred cubic (fcc) and hard ferrites as hexagonal close packed (hcp) structure respectively. Temperature dependence of magnetization in the range of 20-700 degrees C demonstrated distinct presence of soft and hard ferrites as magnetic phases which are characterized by wide difference in magnetic anisotropy and coercivity. Exchange-spring mechanism led these nanocomposite systems to exchange-coupled, which ultimately produced convex hysteresis loops characteristic of a single-phase permanent magnet. Fairly high value of coercivity and maximum energy product were observed for the samples in the optimum calcined conditions with a maximum applied field of 1600 kA/m (2 T).

Synthesis and photoluminescence properties of a novel Sr2CeO4:Dy3+ nanophosphor with enhanced brightness by Li+ co-doping

A series of Dy3+ (0.5-9 mol%) and Li+ (0.5-3 mol%) co-doped strontium cerate (Sr2CeO4) nanopowders are synthesized by low temperature solution combustion synthesis. The effects of Li+ doping on the crystal structure, chemical composition, surface morphology and photoluminescence properties are investigated. The X-ray diffraction results confirm that all the samples calcined at 900 degrees C show the pure orthorhombic (Pbam) phase. Scanning electron microscopy analysis reveals that the particles adopt irregular morphology and the porous nature of the product. Room temperature photoluminescence results indicate that the phosphor can be effectively excited by near UV radiation (290 to 390 nm) which results in the blue (484 nm) and yellow (575 nm) emission. Furthermore, PL emission intensity and wavelength are highly dependent on the concentration of Li+ doping. The emission intensity is enhanced by similar to 3 fold with Li+ doping. White light is achieved by merely varying dopant concentration. The colour purity of the phosphor is confirmed by CIE co-ordinates (x = 0.298, y = 0.360). The study demonstrates a simple and efficient method for the synthesis of novel nanophosphors with enhanced white emission.

Mixture of Fuels Approach for the Synthesis of SrFeO3-delta Nanocatalyst and Its Impact on the Catalytic Reduction of Nitrobenzene

A modified solution combustion approach was applied in the synthesis of nanosize SrFeO3-delta (SFO) using single as well as mixture of citric acid, oxalic acid, and glycine as fuels with corresponding metal nitrates as precursors. The synthesized and calcined powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis and derivative thermogravimetric analysis (TG-DTG), scanning electron microscopy, transmission electron microscopy, N-2 physisorption methods, and acidic strength by n-butyl amine titration methods. The FT-IR spectra show the lower-frequency band at 599 cm(-1) corresponds to metal-oxygen bond (possible Fe-O stretching frequencies) vibrations for the perovskite-structure compound. TG-DTG confirms the formation temperature of SFO ranging between 850-900 degrees C. XRD results reveal that the use of mixture of fuels in the preparation has effect on the crystallite size of the resultant compound. The average particle size of the samples prepared from single fuels as determined from XRD was similar to 50-35 nm, whereas for samples obtained from mixture of fuels, particles with a size of 30-25 nm were obtained. Specifically, the combination of mixture of fuels for the synthesis of SFO catalysts prevents agglomeration of the particles, which in turn leads to decrease in crystallite size and increase in the surface area of the catalysts. It was also observed that the present approach also impacted the catalytic activity of the SFO in the catalytic reduction of nitrobenzene to azoxybenzene.

A Comparative Study on Electrochemical Behaviour of Co3O4 and Co3O4-MWCNTs for Supercapacitors

Co3O4 and Co3O4/MWCNTs were prepared by hydrothermal process under autogenous pressure in Teflon lined autoclave and calcined at 250 degrees C. Both samples were characterized by PXRD, FT-IR, SEM-EDS, TEM & FT-Raman to evaluate their surface and bulk properties. The PXRD pattern of the materials indicated the formation of cubic phase of Co3O4. FT-IR results showed the presence of metal oxygen bond in the samples. The SEM and TEM images of the Co3O4 / MWCNTs indicated spherical and cubic aggregates of metal oxide particles (10-30 nm) decorated both on the surface and inside the tubes of carbon nanotubes. The characteristic Ig and Id (graphitic and defects) Raman bands indicated the retention of tubular structure of MWCNTs even after the deposition of Co3O4. The calcined Co3O4-MWCNTs composites and Co3O4 exhibited specific capacitance of 284 & 205 F/g at a sweep rate of 2mVs(-1) in 6M KOH by cyclic voltammetry. The psuedocapacitance performances of calcined Co3O4-MWCNTs were found to be better than Co3O4. Chronopotentiometric studies made for the materials at a current density of 500mA/g indicated 100% columbic efficiency at 2000th cycle for Co3O4/ MWCNTs which is a better electrode material than Co3O4.

Study on Low Temperature DC Electrical Conductivity of SnO2 Nanomaterial Synthesized by Simple Gel Combustion Method

Nanocrystalline tin oxide (SnO2) material of different particle size was synthesized using gel combustion method by varying oxidizer (HNO3) and keeping fuel as a constant. The prepared samples were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive Analysis X-ray Spectroscope (EDAX). The effect of oxidizer in the gel combustion method was investigated by inspecting the particle size of nano SnO2 powder. The particle size was found to be increases with the increase of oxidizer from 8 to 12 moles. The X-ray diffraction patterns of the calcined product showed the formation of high purity tetragonal tin (IV) oxide with the particle size in the range of 17 to 31 nm which was calculated by Scherer's formula. The particles and temperature dependence of direct (DC) electrical conductivity of SnO2 nanomaterial was studied using Keithley source meter. The DC electrical conductivity of SnO2 nanomaterial increases with the temperature from 80 to 300K and decrease with the particle size at constant temperature.